But historian says dissident threat to peace process is less severe than a year ago

(CNN) -- The summer marching season has long been an annual flashpoint between Northern Ireland's Protestant and Catholic communities, despite the peace process which has brought stability to the province in recent years.

At least 27 police officers were injured in overnight clashes in Belfast, including three hit by shotgun pellets, on the eve of July 12, known as "The Twelth" by Protestants who march to celebrate the victory of English king William III over his ousted Catholic predecessor James II in 1690.

The latest violence was blamed on dissident republicans; groups such as the Real IRA and Continuity IRA who oppose the 1998 Good Friday peace settlement and power-sharing deal negotiated and signed by mainstream republican leaders such as Sinn Fein's Gerry Adams and Martin McGuinness.

"Things are extremely tense, more tense than they have been for some time," journalist Peter Taggart told CNN on Monday.

"There was very serious trouble last year. It erupted at this time and went on for several days and we are expecting worse trouble -- certainly the predictions are that there could be worse violence tonight."

Northern Ireland remains a region divided into two distinct communities; Protestant loyalists, who favor continuing union with the UK, and Catholic republicans in favor of a united Ireland.

Since the mid-1990s, when Sinn Fein, the political wing of the Provisional IRA, entered British-backed negotiations aimed at finding a political settlement to decades of sectarian violence, dissident republicans have carried out bombings and violent attacks in the province, notably the 1998 Omagh bombing in which 29 people were killed.

Those have continued periodically since the IRA decommissioned its weapons in 2005, prompting the Independent Monitoring Commission, which monitors paramilitary activity in the province, to warn in its latest report, published in May 2010, that dissident Republicans were "intent on causing death and serious injury to the people of Northern Ireland."

Martyn Frampton, a lecturer in modern history at Queen Mary, University of London, and the author of a forthcoming book, "Legion of the Rearguard: Dissident Irish Republicanism," said that dissident groups remained a "republican sub culture," with a membership numbering in at least the several hundreds.

But he said there had been a "step change" in the last two to three years caused by dissatisfaction with the peace process.

"It's become clear now that more and more previously quiescent republican areas -- in places such as Belfast, south Armagh and east Tyrone -- appear now to be experiencing some level of dissident momentum," Frampton told CNN. "All the areas that you'd have previously thought of as Provisional republican heartlands really now appear to be under the sway of the dissidents."

Frampton also said there had been an apparent reversal of the previous trend which saw dissident groups fragmenting into various factions, with the Real IRA especially gaining "a degree of momentum and coherence."

Northern Ireland's weak economy could also play to dissidents' advantage with impoverished sink estates creating "reservoirs of discontent" with the peace process, he said.

And while dissidents lack the levels of support enjoyed by the Provisional IRA during the 1970s and 1980s, they seem increasingly well organized within networks that the security services appear to find hard to penetrate. "The simple reality is that it doesn't take very many people to run this type of campaign," said Frampton.

But Paul Bew, Professor of Irish Politics at Queen's University Belfast, said the risk of dissident violence destabilizing the peace process had actually receded in recent months.

Bew said the fact Northern Irish voters from both communities had backed moderate parties in May's UK general election suggested support for the peace settlement remained solid.

"The ability of this sort of terrorism to be effective depends on its ability to set off a political chain reaction throughout the system and to reduce support for the settlement," Bew told CNN.

"My view is that the dissident republican threat is less than I thought it was a few months ago. At the time of the 2009 European elections it looked like that was happening. The general election showed a totally different picture."

Another factor which could prevent a return to the high levels of violence seen in the 1970s and 1980s, Bew said, was that loyalist paramilitaries have so far failed to retaliate to dissident violence.

That depended on loyalists continuing to believe that the British state was committed to defending their interests, he said.

All of this is fragile; all of this could accidentally go awry--Paul Bew, Professor of Irish Politics, Queen's University Belfast

"It's when republicans were seriously active and the British state was proceeding to get out of Ireland that loyalist violence shot up. It's the absence of the second factor, and that we now have a stable constitutional settlement, which means that there has so far been relatively little Loyalist reaction."

A long-negotiated deal over the devolution of policing powers to Belfast, hailed as the "final piece in the devolution jigsaw," has also removed a potentially destabilizing political issue from the stage, Bew said.

But he did warn that continuing attacks on police officers were a "profound" cause for concern. "We have a community style of policing and the more the police come under violent attack the harder it is to sustain the new style of policing," he said.

"All of this is fragile; all of this could accidentally go awry," he added.

Bew said the volatility of the marching season was likely to continue for years to come despite the progress made in other areas towards a peaceful and stable Northern Ireland. But he said there was hope that historic antagonisms could fade in time.

"It's a small place and if you have a lot of Orangemen on the streets on the 12th of July not everywhere they are going to march is 100 percent a Protestant area," he said.

"We are probably stuck with something like this. The broad trend is that you have a diminution of these kinds of flashpoints and it is possible that they would diminish further. But fundamentally the problems caused by the existence of marching culture are going to exist for many summers to come."